BACKGROUND:: The objectives of this study were to develop a murine model of labor and delivery and to use this model to examine whether capsaicin diminishes labor pain and expedites delivery. METHODS:: To develop a murine model of labor pain, the authors identified and compared the incidence of four proposed pain behaviors in 46 mice: (1) No analgesia in labor and the postpartum period, and (2) increasing doses of an analgesic, morphine. The model was then used to examine the impact of topical cervical capsaicin on: (1) labor pain behaviors and (2) labor progress by examining its impact on the time from treatment to delivery of the first pup and on the duration of delivery per pup. The treatment was randomly allocated and the behavioral observation was blinded. RESULTS:: In the absence of analgesia, there was a statistically significant decrease in all four proposed pain behaviors in the postpartum period compared with labor (cumulative 55.0 ± 16.1/h vs. 16.1 ± 8.7/h; P < 0.0001). Additionally, morphine reduced their incidence during labor in a dose-dependent manner (cumulative 55.0 ± 16.1.7/h control, 46.4 ± 15.8 morphine 0.1 mg/kg/h, 34.6 ± 5.6/h, morphine 0.5 mg/kg/h; P = 0.1988, 0.0014). In addition, the incidence of identified pain behaviors was reduced by pericervical capsaicin (cumulative 55.0 ± 16.1.7/h control, 38.9 ± 15.4 capsaicin, P = 0.02). CONCLUSIONS:: In this pilot study, the authors developed a novel mouse model of labor and delivery. Pericervical capsaicin applied days before delivery reduces labor pain behaviors.

* Assistant Professor, Department of Obstetrics and Gynecology, American University of Beirut Medical Center, Beirut, Lebanon, and Adjunct Assistant Professor, Department of Obstetrics and Gynecology, Columbia University Medical Center, New York, New York. † Volunteer, ‡ Senior Research Assistant, Department of Anesthesiology, Columbia University Medical Center. § Professor, Department of Anesthesiology, Columbia University Medical Center. Current position: Department of Anesthesia and Perioperative Care and Department of Obstetrics, Gynecology and Reproductive Medicine, University of California, San Francisco, San Francisco, California.